Optimization of dc feeder rate of rise overcurrent protection settings using delta i cumulative distribution

A novel approach for optimizing the protection settings of DC rate-of-rise overcurrent relays is presented in this paper. It is based on a program developed in Matlab that analyses digitally recorded feeder current data and provides a graphical cumulative distribution profile of the step current increase (Delta I) versus slope (di/dt) characteristics. It was successfully used to enhance the overcurrent protection sensitivity of an existing traction power distribution system without leading to nuisance tripping. The rate-of-rise protection optimization involves the broadening of the DC short circuit detection range while preserving good discrimination between fault and normal rolling stock acceleration currents.